Generic Name

Oxcarbazepine

Mechanism

Oxcarbazepine primarily works by:
• Sodium‑channel blockade – stabilizes inactive state of voltage‑gated Na⁺ channels, reducing repetitive firing in neurons.
• Reducing hyperexcitability – decreases release of excitatory neurotransmitters, dampening seizures.
• Metabolite contribution – the active α‑keto‑valproate metabolite (M5) augments anticonvulsant potency.

The drug’s rapid conversion to its active metabolite allows effective seizure suppression at lower systemic concentrations than carbamazepine.

Pharmacokinetics

• Absorption – Rapid oral absorption; bioavailability ≈ 55 % on an empty stomach, 30 % with food (half‑dose effect).
• Peak plasma – 1–2 h post‑dose.
• Metabolism – Oxidative N‑demethylation to the active M5; minimal CYP450 involvement (≈ 3 % of drug).
• Elimination – Primarily renal excretion (≈ 70 % unchanged); half‑life ≈ 12–18 h (M5 ~ 13 h).
• Drug interactions – Little interaction with enzyme inducers/inhibitors; safe with many anticonvulsants.

Indications

• Partial‑onset seizures (with or without secondary generalization) – first‑line in many centers.
• Benign epilepsy syndromes – e.g., Lennox‑Gastaut.
• Adjunctive therapy – for uncontrolled generalized tonic‑clonic seizures.
• Neuropathic pain – off‑label use in trigeminal neuralgia and post‑herpetic neuralgia in selected cases.

Contraindications

• Hypersensitivity to oxexplanone or its constituents.
• Severe hepatic impairment – contraindicated; metabolite M5 may accumulate.
• Pregnancy – Category D; use only if benefits outweigh risks (off‑label data suggest lower teratogenicity than carbamazepine, but caution remains).
• Hyponatremia risk – especially in elderly or those on SIADH‐promoting drugs.
• Stevens–Johnson syndrome (SJS)/Toxic epidermal necrolysis (TEN) – high vigilance for rash; discontinue immediately.

Dosing

• Initial loading – 300 mg orally twice daily (BID) for the first week.
• Titration – 600 mg BID (≈ 1200 mg total daily) after the first week, increasing every 2–3 weeks as tolerated.
• Maintenance – 600–1200 mg total daily, divided BID; optimum dose individualized.
• Other regimens – 900 mg BID occasionally employed in refractory partial seizures.
• Administration tips
• Take on an empty stomach or with a light snack to avoid reduced absorption.
• Consistency is critical: avoid large variations between doses.

Adverse Effects

Monitoring

• Serum sodium – baseline, then weekly for 2–3 weeks, monthly for elderly >50 y/o.
• Complete blood count – baseline; repeat after 1–2 months if concerns arise.
• Liver & renal function – baseline; repeat if dose adjustment is needed or renal impairment suspected.
• Drug serum levels (optional) – correlate dose and effectiveness, particularly in resistant cases.
• Clinical assessment – seizure frequency, side‑effect profile, pregnancy tests for women of childbearing potential.

Clinical Pearls

• “Why oxcarbazepine beats carbamazepine in pregnancy?”
• Oxcarbazepine’s metabolite is cleared renally, not hepatically; lower rates of teratogenicity in animal studies, though human data remain limited. Use only with informed consent.
• “Avoid the half‑dose food trap!”
• Food dramatically lowers absorption; always advise patients to take the medication either two hours before or after meals for consistent plasma levels.
• “Hyponatremia risk factors”
• Combine with diuretics (esp. thiazides), SSRIs, or appetite suppressants. Elderly patients or those with renal impairment warrant closer sodium monitoring.
• “Rapid titration is a myth”
• Aggressive dose escalation increases adverse effect burden without clear efficacy gains. Follow a conservative titration schedule (≤ 300 mg incremental steps, every 2–3 weeks).
• “Use the Two‑day protocol for dose adjustment”
• For patients moving from long‑term carbamazepine therapy, a staggered switch (introduce oxcarbazepine while tapering carbamazepine over 4–6 weeks) reduces risk of breakthrough seizures.
• “Side‑effect anticipation”
• Ataxia and dizziness are dose‑related and should be a pre‑emptive discussion point when initiating therapy, especially in patients prone to falls.
• “Adapting to hepatic impairment”
• Although contraindicated in severe liver disease, mild hepatic dysfunction may necessitate a modest downtitration (e.g., 300–600 mg BID) and close monitoring of serum levels.
• “SJS/TEN surveillance”
• Educate patients to report any rash within the first 30 days and to seek immediate medical attention; early discontinuation mitigates progression.

This drug card offers a succinct, clinically actionable reference for medical students and practitioners, focusing on key pharmacologic principles and real‑world application tips.